This invention relates to iontophoresis apparatus for applying local anesthetics to selected locations of animal bodies. The apparatus is useful particularly for applying local anesthetics in the external ear of humans and is described particularly with reference to such application. No limitation thereby is intended, however, since the apparatus with suitable modification may be used for the application of local anesthetics to any and all other body areas requiring local anesthetic and burdened by potentially acutely painful conditions, for example the area surrounding an ingrown toenail.
As is well known, the external auditory meatus (ear canal) includes a highly sensitive body area which is prone to infection and other physical failings requiring anesthesia before the indicated surgical or medical treatment may be performed. Serious attempts to anesthetize the ear began with the advent of cocaine in 1870. However, topical applications of this anesthetic have been disappointing from the standpoint of lack of effectiveness as well as from that of the production of adverse results. Similarly, dibucaine, tetracaine, cyclaine and phenol compounds all have been shown to be ineffective as local anesthetics for the purpose of anesthetizing the ear and in addition may cause undesirable side effects such as local tissue damage, allergic or toxic reactions, or contact dermatitis.
As a consequence, at the present time the procedure for obtaining anesthesia in the vast majority of ear surgeries is by local injection of anesthetic agents. This procedure is often as painful as the surgical pain it is designed to alleviate (e.g., the pain of a myringotomy, or piercing of the tympanic membrane). Consequently there is need for a painless procedure for anesthetizing sensitive areas such as the ear canal and drum. This need is particularly acute in the case of children.
It also is well known that iontophoresis when properly administered is an effective and painless method for driving anesthetic agents into the skin and thereby producing local anesthesia.
Iontophoresis is a process which utilizes direct electrical current to drive ionized chemical agents through the intact skin. For example, in aqueous media lidocaine hydrochloride disassociates into ions. The lidocaine ions responsible for its anesthetic action carry a positive electrical charge. Accordingly the anesthetizing lidocaine ions can be driven through the skin by the repelling action of the positive pole of a battery. Thus when iontophoresing lidocaine through the skin, the electrode contacting the lidocaine solution must be connected to the positive pole of the battery while the ground electrode which contacts the skin at some distant point is connected to the negative pole and provides a return path for the direct current.
The application of the techniques of iontophoresis to anesthetizing the auditory canal and ear drum was attempted as early as 1911. However, when considered from a practical standpoint, the results were unsatisfactory because the patients became vertiginous during and after treatment and some suffered permanent hearing losses. Also, the 1911 procedure was not free from pain and physical discomfort.
A further complicating circumstance is the fact that when the body is the medium for iontophoresis, fluctuations in current intensity often result which may produce pronounced symptoms of vertigo and pain, as well as unpleasant tingling sensations. Burns may be produced when the electrodes are improperly applied.
Fluctuations in current intensity are difficult to avoid when practicing iontophoresis. The intensity of the current passing through the body is a function of the electrical resistance of the body. This varies from patient to patient. In a given patient it also varies with such factors as nervous tension, fatigue, physical condition, emotions, sleep and mental state. This creates a problem, since if there is too little current, the anesthesia may be incomplete. if there is too much, there may be patient discomfort.
Accordingly it is the general purpose of the present invention to provide iontophoresis apparatus and method for applying local anesthetics to selected areas of the body, and especially to the ear drum and outer ear canal.
It is a particular object of the present invention to provide iontophoresis method and apparatus for local anesthesia the use of which is highly efficient in effectively anesthetizing selected body areas, without the accompaniment of undesirable side effects such as pain and vertigo or local tissue damage caused by burning or chemical action.
A further object of the present invention is the provision of iontophoresis apparatus for applying local anesthetics which apparatus is relatively simple and inexpensive in construction, reliable in operation, universally applicable with suitable modifications to anesthetizing various areas of the body, foolproof in its operation, and easily operated by personnel of average medical training readily available in any medical center.
Still other objects of the present invention are the provisions of iontophoretic anesthetizing apparatus which is sanitary in use; is reusable; will not shock the patient; permits the operator visually to inspect the site; does not damage the inner ear in any way; can be used with a wide variety of anesthetics; and is easily assembled and used.